The present invention relates to a process for coating articles, wherein the coating comprises a polymer having desirable characteristics regarding adherence to the substrate, durability, softness, hydrophilicity, lubricity, wettability, biocompatibility and permeability. More particular, the present invention relates to a process for coating an article, such as a biomedical material or article, especially ophthalmic devices such as ocular implants, artificial corneas and contact lenses including an extended-wear contact lens, wherein at least a part of the coating comprises a polymer having a xe2x80x9cbottle-brushxe2x80x9d or comb type structure. The inventive coatings are obtainable from novel preformed comb-type polymers having photoreactive groups linked pendently to the polymer backbone by applying them onto a substrate surface and then fixing them using irradiation. The resulting coatings are composed of hairy highly hydrophilic polymer chains or highly branched polymer chains which form covalently bound and loosely crosslinked highly water containing networks with an overall large void volume.
A variety of different types of processes for preparing hydrophilic polymeric coatings on an xe2x80x9cinertxe2x80x9d hydrophobic substrate have been disclosed in the prior art. For example, WO 99/57581 discloses to first of all provide the article surface with covalently bound photoinitiator molecules, coating the modified surface with a layer of a polymerizable macromonomer and then subjecting it to a heat or radiation treatment whereby the macromonomer is graft polymerized thus forming the novel article surface. The known surface modification process is applicable only to articles having a functionalized surface, that is to say, the surface of the article either inherently contains functional groups or the functional groups have to be introduced previously by a plasma treatment or the like.
A plasma treatment as part of a high volume production requires a considerable investment in equipment and is furthermore difficult to be integrated in an automated production process. For example, a plasma treatment requires usually high vacuum conditions; in addition the article to be treated must be dry before exposure to the plasma. Thus, a polymeric article such as a contact lens that is wet from prior hydration or extraction must be dried previously, thereby adding time in the overall lens production process as well as imposing added costs of obtaining a drying equipment. In addition, drying a hydrogel type contact lens often affects its shape and optical quality in an irreversible manner. Therefore, it would be highly desirable to initiate the covalent binding of a hydrophilic layer to an xe2x80x9cinertxe2x80x9d surface such that the plasma treatment is avoided and replaced by a technique which is easy to perform with standard equipment under ambient conditions, and which is thus more feasible for an automated production process.
Surprisingly, now there have been found novel branched reactive polymer derivatives which are able to react with the surface of articles being devoid of functional groups. By means of said novel polymers it is possible to obtain articles, particularly biomedical devices such as, for example, contact lenses, with an improved wettability, water-retention ability, surface lubricity and biocompatibility as well as high wearing comfort and longterm overall on-eye performance.
The present invention therefore in one aspect relates to a process for coating a material surface comprising the steps of:
(a) applying to the material surface one or more different comb-type polymers comprising a polymer backbone and side chains pendently attached thereto, wherein at least a part of the side chains carry a triggerable precursor for carbene or nitrene formation; and
(b) fixing the polymer(s) onto the material surface using heat or radiation, in particular radiation such as UV or visible light.
The polymers that are useful in the process of the invention are novel and represent a further object of the invention.
The backbone of the polymers according to step (a) of the process may be, for example, a polyvinyl homo- or copolymer, a polyethylene imine, a polypeptide, a polyether or a polysaccharide. Examples of suitable side chains that are attached to the polymer backbone are functional hydrophilic homo- or cotelomers, polyalkylene oxides, oligosaccharides or oligopeptides, and at least a part of said side chains carry at least one triggerable precursor for carbene or nitrene formation.